Procurement Guide

Inconel, Hastelloy, Monel, Titanium Fasteners: Complete Procurement Guide

By Ragnar Metals & Tubes Engineering Team • October 14, 2026 • 9 min read

When stainless steel fasteners fail due to corrosion, elevated temperature, or chemical attack, the next step is nickel alloys or titanium. But Inconel, Hastelloy, Monel, and Titanium each serve different failure modes — choosing the wrong one wastes money; choosing the right one eliminates a recurring maintenance problem. This guide gives you the data to decide.

When Standard Stainless Fasteners Are Not Enough

316L stainless steel fasteners cover most industrial applications, but they fail in specific situations:

• Chloride stress-corrosion cracking (SCC): SS 316L fails in hot chloride environments above ~60°C. Duplex or nickel alloys are needed.
• Pitting in seawater at elevated temperatures: SS 316L pits aggressively in hot seawater (>30°C). Super duplex or 6Mo/Inconel is required.
• Sulphuric acid or hydrochloric acid service: SS 316L has poor resistance to reducing acids. Hastelloy C276 or Monel 400 is needed.
• High-temperature service (>650°C): SS 316L loses strength and oxidises. Inconel 625 or 718 is required.
• Galvanic coupling in seawater: Titanium Grade 2 avoids galvanic corrosion when coupled to Ti structures.

Inconel 625 Fasteners (UNS N06625)

Best applications: Offshore topside bolting, subsea ROV panels, heat exchanger bolting in aggressive chemicals, gas turbine exhaust flanges, cryogenic applications.

Hastelloy C276 Fasteners (UNS N10276)

Best applications: Scrubber bolting (FGD systems), chemical reactor flanges where mixed acid exposure occurs, HCl pickling plant equipment, waste treatment tanks.

Monel 400 Fasteners (UNS N04400)

Best applications: Seawater desalination plant fasteners, offshore platform deck bolting (tidal zone), hydrofluoric acid alkylation unit piping flanges, marine propeller shaft bolts.

Titanium Grade 2 and Grade 5 Fasteners

Important limitation: Titanium fasteners must never be used in contact with oxidising acids such as fuming nitric acid — this causes pyrophoric ignition. Titanium is also susceptible to crevice corrosion in reducing acid environments.

Grade Selection Quick Reference

Procurement Checklist for Nickel Alloy Fasteners

1. Confirm the UNS number (not just the trade name) — "Inconel" is a Huntington Alloys brand; the actual alloy matters
2. Specify the ASTM standard and condition (annealed vs. age-hardened)
3. Require EN 10204 3.1 MTC with full heat analysis and mechanical properties
4. Request PMI (positive material identification) report — 100% PMI for critical-service fasteners
5. Confirm NACE MR0175 compliance if sour service is involved — hardness test per lot
6. Specify thread form (ASME B1.1 UNC/UNF for US projects; ISO metric for European/Asian projects)
7. Check for Controlled Material marking if project is under pressure vessel code (ASME Section VIII)

Related pages: All Fasteners • Nickel Alloys Comparison • Special Grades